FIG. 1 illustrates a prior art multi-phase switching power supply with output current sensing as disclosed in U.S. Pat. No. 6,683,441. The system of FIG. 1 includes a controller 20 that generates switching control signals SC1 and SC2 to drive switch circuits 10 and 12, thereby controlling the amount of power delivered to the load 22 through inductors 14 and 16. Additional circuitry would typically be included to sense the output voltage VOUT so the controller can modulate the switch signals to maintain a constant output voltage regardless of the amount of current consumed by the load. The sensed output voltage is usually combined with an input signal to generate an error signal that is applied to the controller for closed-loop control of the output.
The system of FIG. 1 also includes a current sensing circuit 18 to generate a signal VCS that provides a measure of the total combined output current delivered to the load. The current sense signal may be used in numerous ways. For example, it may be used to provide over-current shutdown, it may be used to implement current-mode regulation, or it may be combined with voltage feedback to establish a droop impedance for adaptive voltage positioning (AVP) control schemes.
In some switching power supply systems, the current sense signal VCS may also be used to monitor the power consumed by the load. Since power may be computed by multiplying output voltage by output current, conventional techniques for power monitoring typically involve the use of an analog multiplier circuit (such as a Gilbert cell), or conversion of analog signals to digital information with multiplication performed in the digital domain. To facilitate power monitoring, existing systems may provide a current output signal that is an amplified version of a measured current signal, where amplification is either done digitally or with a simple continuous analog amplifier. Existing methods for producing current signals are straightforward, but require amplifiers with good electrical parameters. Also, to produce a ground referenced signal requires differential amplifiers or sampling techniques since most current sensing elements are not ground referenced or only have pertinent information part of the time.